Synthesis and sintering of Gd-doped CeO₂ electrolytes with and without 1 at.% CuO dopping for solid oxide fuel cell applications

Nano-sized Ce_0.8Gd_0.2O_2-δ and Ce_0.79Gd_0.2Cu_0.01O_2-δ electrolyte powders were synthesized by the polyvinyl alcohol assisted combustion method, and then characterized by powder characteristics, sintering behaviors and electrical properties. The results demonstrate that the as-synthesized Ce_0.8Gd_0.2O_2-δ and Ce _0.79Gd_0.2Cu_0.01O_2-δ possessed similar powder characteristics, including cubic fluorite crystalline structure, porous foamy morphology and agglomerated secondary particles composed of gas cavities and primary nano crystals. Nevertheless, after ball-milling these two powders exhibited quite different sintering abilities. A significant reduction of about 400 °C in densification temperature of Ce_0.79Gd _0.2Cu_0.01O_2-δ was obtained when compared with Ce_0.8Gd_0.2O_2-δ. The Ce _0.79Gd_0.2Cu_0.01O_2-δ pellets sintered at 1000 °C and the Ce_0.8Gd_0.2O _2-δ sintered at 1400 °C exhibited relative densities of 96.33% and 95.7%, respectively. The sintering of Ce_0.79Gd _0.2Cu_0.01O_2-δ was dominated by the liquid phase process, followed by the evaporation-condensation process, Moreover, Ce_0.79Gd_0.2Cu_0.01O_2-δ shows much higher conductivity of 0.026 S cm^-1 than Ce_0.8Gd _0.2O_2-δ (0.0065 S cm^-1) at a testing temperature of 600 °C.